Currently, a wireless communication system can enhance spectrum efficiency by optimizing a transmission mode of a mobile station in accordance with a channel status. However, the transmission mode of the mobile station may not be optimized depending on the channel status in the wireless communication system.
First of all, the transmission mode of the mobile station may not be optimized for an initial access process. In order to perform initial access, the mobile station transmits a preamble to a base station and waits for a random access response message. If the random access response message is received from the base station, the mobile station default request information to the base station. Then, the base station decodes the information received from the mobile station. In other words, since the base station does not know information on configuration or transmission mode of the mobile station for the initial access process, the mobile station transmits data in a default transmission mode.
However, the mobile station may select a proper transmission mode depending on a channel status and transmit data in accordance with the selected transmission mode, whereby frequency gain and diversity gain may be obtained.
Second, the transmission mode of the mobile station may not be optimized for a non-scheduled transmission process. The non-scheduled transmission is used for transmission of low latency or operation of a short active time of the mobile station. Since the base station cannot know information on configuration or transmission mode of the mobile station even for the non-scheduled transmission process, the mobile station transmits data in a default transmission mode, so that the base station may decode the data received from the mobile station.
For the initial access process and the non-scheduled transmission, the base station cannot know configuration of the mobile station and channel features. However, the mobile station may know channel features, and may select a proper transmission mode in accordance with channel features.
However, if the mobile station transmits data in a default mode regardless of the channel status for the initial access process and the non-scheduled transmission in accordance with the related art, a problem occurs in that resource efficiency is deteriorated.